Lower molecular weight alcohols and ethers such as isopropanol (IPA) and diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have high blending octane numbers. In addition, by-product propylene from which IPA and DIPE can be made is usually available in a fuels refinery. An important aspect of research in the petroleum industry relates to processes to produce high octane gasolines blended with lower aliphatic alkyl ethers as octane boosters and supplementary fuels. C.sub.5 -C.sub.7 methyl alkyl ethers, especially methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME) have been found particularly useful for enhancing gasoline octane, as has diisopropyl ether (DIPE). Improvements to the processes related to the production of these ethers are matters of high importance and substantial challenge to research workers in the petroleum refining arts.
The catalytic hydration of olefins, particularly C.sub.3 and C.sub.4 olefins, to provide alcohols and ethers is a well-established art and is of significant commercial importance. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,262,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,848; 3,989,762, among others.
The production of ether from secondary alcohols such as isopropanol and light olefins is known. As disclosed in U.S. Pat. No. 4,182,914, DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cation exchange resin as catalyst. Recently, processes for the hydration of olefins to provide alcohols and ethers using zeolite catalyst have been disclosed by Bell et al. in U.S. patent applications Ser. Nos. 336,582 filed Apr. 10, 1989; 336,504 filed Apr. 11, 1989; 139,569 filed Dec. 30, 1987; 265,324 to Wang et al. filed Oct. 27, 1988; and 139,566 (allowed) to Wang filed Feb. 30, 1987. These applications are incorporated herein in their entirety by reference.
In the conversion of a water feedstream and a C.sub.3 hydrocarbons feedstream comprising propene and propane to DIPE and IPA, the conversion per pass is typically about 60%. Recycling of the unreacted C.sub.3 's unavoidably involves compression and recycling of unreacted propene to the etherification reactor. This, in turn, requires feeding and operating the reactor at higher pressures in order to maintain an effective propene partial pressure in the vessel; a situation inimical to improved process economics. Also, separating IPA from the reaction effluent and recycling IPA to the etherification reactor as typically carried out presents additional process problems.
It is an object of the present invention to provide an integrated process to produce DIPE and gasoline boiling range hydrocarbons.
It is another object of the present invention to provide a process for the production of DIPE and gasoline boiling range hydrocarbons without recycling unreacted C.sub.3 hydrocarbons.
Yet another object of the present invention is to provide an improved means for separating and recycling IPA in the DIPE process.